Actuators may be viewed as devices which supply short but intense bursts of pressure, whereas igniters supply intense bursts of heat. Actuator and igniter structures are quite similar. Each comprises a header having two or more insulated electrodes electrically connected by a bridgewire. A charge cavity is situated atop the bridgewire surface of the header. The charge cavity may either be integral to the header shell or may comprise a can welded to the top of the header. The charge cavity is filled with pyrotechnic or explosive powder and a closure disk is welded to either the shell or the can to contain the powder and create a hermetic seal. Function times for these devices are thought to be 0.00005 second or less.
Actuators and igniters of this type are primarily used in aerospace applications. Examples include explosive bolts, ejection seats, explosive valves, igniters to start rocket motors, and deployment systems for parachutes. Actuators are also used in air bag restraint systems for automobiles.
Means to produce a rapid release of pressure can be used in other applications as well. For instance, air guns and gas guns may require such a means as well as methods of projecting projectiles by a rapid release of pressure.
A need to test closure disks at high rates of change of pressure exists. It is known that igniters exhibit variable work output upon functioning. It is also known that as pressure of a gas over a pyrotechnic increases, the rate of burn also increases. In addition, the pressure differential at which a closure disk bursts is dependent on the rate of pressurization. Since the burn rate depends upon the pressure differential, it is difficult to test for burst pressure differential of a closure disk by producing pressure using pyrotechnics. A need therefore exists for means of rapidly producing a pressure differential without pyrotechnics.
A hand pump such as a hand-operated hydraulic pump has previously been used to test closure disks. Pressure is applied to a closure disk by means of a hydraulic fluid. Problems exist with the hand pump method of testing in that the minimum time of rupture for closure tests is on the order of several seconds.
Another device which might be used to test closure disks is the gas gun or shock tube, although the inventors have no knowledge of tests having been performed on closure disks with this device. This type of device requires an explosive charge used to drive a piston or flyer down a tube. The piston or flyer compresses gas behind a diaphragm until the diaphragm ruptures resulting in a shock wave. The shock wave travels down the tube creating high pressures and temperatures reaching 2000.degree. C. These instruments usually have lengths of 20 feet or longer and are very expensive. A need therefore exists for a closure disk tester which ruptures a closure disk without requiring lengthy rupture times, high temperatures, or high costs.